Multi-channel tuner



Dec. 11, 1962 T. BARNES MULTI-CHANNEL TUNER Filed Nov. 28, 1960 m m w JAlik/ELLYN 7. fink/v55 Arron/V573 ,7 meant Patented Dec. 11, 1962 free3,068,384 MULTI-CHANNEL TUNER Llewellyn T. Barnes, Freeport, N.Y.,assigncr of thirtythree and one-third percent to Charles T. Barnes,Freeport, N.Y., and thirty-three and one-third percent to John F. Woog,Garden City, NY.

Filed Nov. 28, 1960, Ser. No. 71,974 7 Claims. (Cl. 317-249) Thisinvention relates to capacitors, and in particular to an improvedmulti-channel tuning capacitor.

In various communication applications it is desirable to effect coarsetuning by shifting discontinuously from one frequency channel toanother, but then to tune continuously within the frequency range of theselected channel for fine adjustment. For this purpose multichanneltuners are provided which have several alterna tive predeterminedcapacitance ranges, each corresponding to one of the frequency channels,with provision for adjustment of capacitance within each such range.

It is an object of this invention to provide an improved tuner of theforegoing type which provides the advantages of simplicity, compactness,rugged construction, ease and economy of manufacture, and ease andaccuracy of calibration and tuning. As a further object of theinvention, improved performance is achieved by a novel constructionwhich provides electrostatic shielding between the electrodescorresponding to the several channels.

In accordance with an illustrative embodiment of the invention, there isprovided a capacitor comprising a supporting tube formed with at leastone axial slot opening into the interior thereof, an elongated fixedelectrode having a dielectric coating bonded to one face thereofdisposed axially within each such slot with the dielectric coatingfacing the supporting tube interior, and another electrode disposedwithin the supporting tube and movable axially for adjustment ofcapacitance.

The foregoing brief summary, as well as additional features and objectsof the invention, will be best appreciated by reference to the followingdetailed description, when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a perspective view of a multi-channel tuner in accordance withthis invention;

FIG. 2 is a longitudinal section of the tuner of FIG. 1; and,

FIG. 3 is an enlarged transverse section of the tuner of the previousfigures, taken along the lines 33 of FIG. 2.

Referring in detail to the drawings, FIG. 1 shows a multi-channel tuner18 in accordance with this invention. As best seen in FIG. 2, the tunerincludes a hollow, open supporting tube 12 fabricated of an electricallyinsulating material such as any ceramic. At one end of the supportingtube 12 is inserted a hollow tubular metal plug 14 which serves to mountthe tuner on a grounded chassis panel. The plug 14 is formed With athickened barrel 16 which is inserted into the tube 12 and is sized fora tight fit therewith. A flange 18 formed a on the plug 14 abuts the endof the tube 12 to limit insertion thereinto. An externally threadedcollar 20 projects outwardly to pass through a mounting aperture formedin a chassis panel 2, and receives a lock washer 24 and hexagonal nut 26which cooperate to secure the tuner to the chassis panel 22 in theconventional manner. This mounting arrangement also serves to makeelectrical contact between the chassis panel 22 and the plug 14 so thatthe latter is at ground potential.

The plug 14 is formed with a cylinder 28 of reduced size which projectspartway into the interior of the supporting tube 12 and terminates in anend wall 30. The

latter is formed with a square aperture 30a which acts as 'a slidebearing for a square reciprocating shaft 32. The shaft 32 has a threadedtip 34 to which is secured, by means of a conventional nut and washer,the central web 36 of a cylindrical metal piston 38. This piston servesas the movable electrode of the tuner 18 and is axially reciprocablealong the interior of supporting tube 12 to vary the capacitance forfine tuning within each channel. The piston 38 fits closely but slidablywithin the bore of Supporting tube 12 so that the tube interior providesa further bearing surface for axial reciprocation of the piston 38 andshaft 32. The structure described also serves to establish electricalcontact from the chassis panel 22 through the plug 14 and shaft 32 tothe elec trode piston 38, so as to ground that side of the capacitor.

Axial movement of the electrode piston 38 is achieved by means of abacklash-free drive housed within the bore of plug 14. The end ofreciprocating shaft 32 which passes through opening 30a and into thebore of plug 14, terminates in a short externally threaded shank 48 ofsomewhat larger diameter. The shank 40 is screwed into the internallythreaded bore of a cylindrical nut 42 which is rotatably mounted withinthe bore of plug 14. Rotation of the cylindrical nut 42 is thustranslated by the threaded connection into reciprocation of the assemblyof the shank 40, shaft 32, and piston 38. The square cross-sectionalshapes of shaft 32 and the opening 38a through which it passes serve tohold this assembly against rotation with the cylindrical nut 42. The endof the cylindrical nut 42 nearest the end wall 30 has an outsidediameter selected to make a freely rotatable bearrelative to each other.

ing contact with the bore of plug 14.

At the other end of the cylindrical nut 42, however, its outsidediameter is reduced to provide a clearance space between the nut 42 andthe bore of plug 14 for the nonbacklash mechanism, which includes acylindrical sleeve 44 and a helical compression spring 46. Thecylindrical nut 42, though rotating as a unit, is split longitudinally(along the division line seen in FIG. 2) into two segments 42a and 4211which are displaceable longitudinally The portion of lower segment 42bwhich is of thicker outside diameter is somewhat longer than thecorresponding portion of upper segment 42a, so that the sleeve 44 isthrust against the thicker portion of the lower segment, but not againstthat of the upper segment, by the pressure exerted thereon by one end ofspring 46. This causes the two segments 42a and 42b to be displacedlongitudinally from each other to the extent that their threadedengagement with shank will allow, thereby keeping both segments 42:: and42b tight against the threads of the shank 40 at all times, to absorbany looseness in the threaded connec .tion which might otherwise giverise to backlash in the fine tuning.

Operator control over the driving movement is achieved by means of athumb wheel 48 which is mounted outside the tuner 10 and in front of thechassis panel 22 for access by an operator. The wheel 43 is atfixcd to ashaft 50 which is journaled in an insert 52 threaded into the front endof the bore of plug 14. A driver member 54 secured to the end of shaft50 inside the bore of plug 14 is formed with cleats 56 projecting intorecesses in the cylindrical nut 42 to make the desired rotary drivingconnection thereto actuate the mechanism which drives the movableelectrode 38. A flange 58 formed on the driver 54 receives the thrust ofthe other end of spring 46, thus keeping the latter in a state ofcompression to maintain the anti-backlash pressure against sleeve 44.The presure of spring 46 against flange 58 also serves to press aconical face 54a of driver 54 against a correspondingly shaped face ofthe insert '52 to deter accidental movement of the capacitanceadjustment drive.

In accordance with this invention, the end of supporting tube 12 nearestthe movable electrode piston 33 is formed with a number of axiallyextending slots 6% which are spaced from each other circumferentiallyabout the tub-e. Each such slot 60, as best seen in FIG. 3, has a depthextending entirely through the thickness of the wall of supporting tube12, and the opposing sides of each slot 60 have surfaces 62 which slopein such a direction that they converge toward each other at both theexterior and interior surfaces of the tube wall. Each slot 662 opensthrough the rear end wall of the supporting tube 12, as at 64, to permitaxial insertion of an elongated electrode plate 66 into each slot fromthe rear thereof.

A separate electrical connection is made to each of tile fixed electrodeplates 66 by means of a lead 72. These leads are lengths of stiff wirewhich radiate from the tuner 10. The inner ends 74 of leads 72 terminatein electrical contact with the respective fixed electrode plates 66 andare secured thereto in the following manner. The inner ends 74, whichare of reduced diameter, are inserted within frusto-conical openings inthe respective fixed electrode plates 66 which taper radially outwardly,and the ends 74 are then upset and are thereby spread to dovetail withthe taper of the electrode plate openings and thus prevent outwardretraction of the leads 72. Inward movement of the leads 72 is preventedby the abutment against the outer surface of the electrode plates 66 bythe shoulder 76 formed by the reduced diameter of the tips 74.

The fixed electrode plates 66 are mounted in the slots 60 near theinterior surface of the wall of tube 12 so that they are very close tothe movable electrode piston 38, and a capacitance is thus developedtherebetween. A thin dielectric coating 78 is bonded to the inwardlyfacing surface of each fixed electrode plate 66. The coating 78preferably consists of a thin layer of glass which is fired by wellknown techniques to the inner surfaces of the electrode plates 66 afterthe loads 72 have been secured thereto. ground and lapped to the precisethickness necessary to produce the desired different capacitance rangefor each such fixed electrode. The end-insertion feature of theconstruction described makes it easy to insert the electrode plates 66into their respective slots 6t] for repeated trials and then withdrawthem each time for additional grinding and lapping during themanufacture and calibration of the tuner 10. A plastic cap 79 may beremovably snapped into place to seal 01f the rear of the tube 12. afterthe calibration process is completed.

Also inserted and withdrawn axially together with the fixed electrodeplates are respective cover panels 80 fabricated of any fairly rigidinsulating material, for example a hard plastic, and formed withopenings through which the leads 72 pass. The cover panels 86, inaddition to closing off the slots 60, form part of an assembly forpositioning the fixed electrode plates 66 accurately with respect to theelectrode piston 38. The cover panels 86 are mounted near the exteriorsurface of the support.- ing tube 12, while the fixed electrode plates66, as was noted, are mounted near the inside surface. Both the coverpanels 86 and fixed electrode plates 66 are formed with tapered sideswhich, when the two are spread as far apart as possible, dovetail withthe tapered sides 62 of the slots 69 in such fashion that outwarddisplacement of the cover panels 84 and inward displacement of the fixedelectrode plates 66 is limited by engagement therewith. Then, to insurethat these elements are kept spread to these limits so that th electrodeplates 66 are held fixed in their inwardmost position, small coilsprings 82 mounted between the respective cover panels 80 and fixedelectrode plates 66 operate compressively therebetween. The coil springs82 surround the leads 72 in the region be tween the cover panels 86 andfixed electrode plates 66, so that the leads '72 serve as guides whichhold the coil The glass coating 78 is then carefully springs 32 inplace. Adjacent these springs 82 the cover panels 36 may be formed withrecesses receiving one end of the springs as shown in the drawing, so asto accommodate a somewhat longer spring in the space between the coverpanels 556 and the fixed electrode plates 66. it will be apparent thatthe springs 82 require that upon Withdrawal and insertion of the fixedelectrode assemblies, as for example during the manufacture andcalibration of the tuner 16, the cover panel St] and fixed electrodeplate 66 be squeezed together somewhat in order to be withdrawn from orinserted into the slots 60, after which they may be released to assumethe positions which they are biased by such springs 82.

Each of the fixed electrodes 66 corresponds to a different frequencychannel to which the capacitor may be tuned. In order to shield thesefixed electrodes from each other so that their capacitance is developedprimarily with respect to the movable electrode 38, there is provided agrounded shielding cage including a number of conductive wires 84, onebetween each of the fixed electrodes 66 and those on either side of it.The wires 84 are embedded in the ceramic supporting tube 12 at the timeof its manufacture, and they extend the length thereof and protrude fromthe forward end. The protruding ends of wires 84 are tightly receivedwithin apertures in the flange 18 of grounded plug 14, so as to makeelectrical contact therewith for holding the shielding cage at groundpotential. The presence of this mode of ground potential betweenadjacent fixed electrodes 66 serves to insulate them from theelectrostatic forces that they would otherwise exert on each other. Acircular wire ring 86 is mounted on the inner face of the cap 79 andengages and contacts the rear ends of the wires 84 when the cap 79 isinserted in the tube 12.

It will now be appreciated that the novel structure of the tuner of thisinvention provides numerous advantageous features, among which are theelectrostatic shielding feature, the ease of removal and replacement ofthe fixed electrode assemblies, the accurate method of calibration, andthe exactness of tuning, as well as the overall simplicity, compactness,and ruggedness of the tuner construction and the ease and economy of itsmanufacture.

A latitude of modification, substitution and change is intended in theforegoing disclosure and in some instances some features of theinvention will be used without a use of other corresponding features.Accordingly, the claims herein should be construed broadly and in amanner consistent with the spirit and scope of the invention.

What I claim is:

1. A variable capacitor comprising a supporting tube formed with anaxial slot opening into the interior thereof and through one end thereofto permit axial insertion of an electrode into said slot, an elongatedelectrode having a dielectric coating bonded to one face thereofdisposed axially within said slot with said dielectric coating facingsaid supporting tube interior, cover means closing off said slot at saidone supporting tube end, and another electrode disposed within saidsupporting tube and movable axially for adjustment of capacitance, andspring means disposed between said cover means and said elongatedelectrode urging said elongated electrode towards said anotherelectrode.

2. A variable capacitor comprising a supporting tube formed with anaxial slot opening into the interior thereof, an elongated electrodeplate disposed axially within said slot, a lead radiating from saidsupporting tube and making electrical contact with said electrode plate,a dielectric coating bonded to the surface of said electrode platefacing said supporting tube interior, another electrode disposed withinsaid supporting tube and movable axially for adjustment of capacitance,and spring means engaging said elongated electrode plate urging saidelongated electrode plate toward said another electrode.

3. A variable capacitor comprising a supporting tube formed with anaxial slot extending entirely through the wall thereof, the oppositesides of said slot converging toward each other at both the exterior andinterior surfaces of said supporting tube, an elongated insulating coverpanel disposed axially within said slot adjacent the exterior surface ofsaid supporting tube and shaped to engage said outwardly converging slotside portions to limit outward movement thereof, an elongated fixedelectrode plate disposed axially within said slot adjacent the interiorsurface of said supporting tube and shaped to engage said inwardlyconverging slot side portions to limit inward movement thereof, a coilspring positioned between said cover panel and said electrode plate tothrust thereagainst for biasing said electrode plate to its inwardmostposition, said cover panel being formed with an opening in alignmentwith the center of said coil spring, a lead radiating from saidsupporting tube passing through said cover panel opening and said coilspring center and making electrical contact with said electrode plate, adielectric coating bonded to the surface of said electrode plate facingsaid supporting tube interior, and another electrode disposed withinsaid supporting tube and movable axially for adjustment of capacitance.

4. A variable capacitor comprising a supporting tube formed with anaxial slot extending entirely through the wall thereof, the oppositesides of said slot converging toward each other at both the exterior andinterior surfaces of said supporting tube, an elongated insulating coverpanel disposed axially within said slot adjacent the exterior surface ofsaid supporting tube and shaped to engage said outwardly converging slotside portions to limit outward movement thereof, an elongated fixedelectrode plate disposed axially within said slot adjacent the interiorsurface of said supporting tube and shaped to engage said inwardlyconverging slot side portions to limit inward movement thereof, a coilspring positioned between said cover panel and said electrode plate tothrust thereagainst for biasing said electrode plate to its inwardrnostposition, said cover panel and electrode plate being formed withopenings in alignment with the center of said coil spring, a leadradiating from said supporting tube passing through said cover panelopening and said coil spring center and formed with a tip secured withinthe opening of said electrode plate to establish electrical contacttherewith and prevent outward extraction of said lead, a dielectriccoating bonded to the surface of said electrode plate facing saidsupporting tube interior, and and another electrode disposed within saidsupporting tube and movable axially for adjustment of capacitance.

5. A multi-channel tuner comprising an electrically insulatingsupporting tube open at one end and formed with axial slots spacedcircumferentially thereabout, elongated electrodes within saidrespective slots each corresponding to a frequency channel, anelectrically conductive plug secured within said supporting tube openend for mounting said capacitor on a chassis and establishing electricalcontact therewith, electrically conductive wires embedded in saidsupporting tube extending axially between said slots and terminating incontact with said plug for electrostatic shielding of said fixedelectrodes, another electrode disposed within said supporting tubespaced from said elongated electrodes and mounted on said plug inelectrical contact therewith to ground one side of said tuner andaxially movable thereon for fine tuning within each frequency channel,and spring means engaging said elongated electrodes urging saidelongated electrodes towards said another electrode.

6. A variable capacitor comprising a supporting tube formed with anaxial slot extending entirely through the wall thereof, the oppositesides of said slot convergin toward each other at both the exterior andinterior sur faces of said supporting tube, an elongated insulatingcover panel disposed axially within said slot adjacent the exteriorsurface of said supporting tube and shaped to engage said outwardlyconverging slot side portions to limit outward movement thereof, anelongated electrode plate disposed axially within said slot adjacent theinterior surface of said supporting tube and shaped to engage saidinwardly converging slot side portions to limit inward movement thereof,and another electrode disposed Within said supporting tube and movableaxially for adjustment of capacitance.

7. A variable capacitor comprising a supporting tube formed with aplurality of spaced axial slots extending entirely through the wallthereof, the opposite sides of each of said slots converging toward eachother at both the exterior and interior surfaces of said supportingtube, elongated insulating cover panels disposed axially within each ofsaid slots adjacent the exterior surface of said supporting tube andshaped to engage said outwardly converging slot side portions to limitoutward movement thereof, elongated electrode plates disposed axiallywithin said slots adjacent the interior surface of said supporting tubeand shaped to engage said inwardly converging slot side portions tolimit inward movement thereof, spring means positioned between saidcover panels and said electrode plates to thrust thereagainst forbiasing said electrode plates to their inwardmost positions, and anotherelectrode disposed within said supporting tube and movable axially foradjustment of capacitance.

References Cited in the file of this patent UNITED STATES PATENTS2,688,177 Wagner Sept. 7, 1954 2,760,127 Duncan Aug. 21, 1956 FOREIGNPATENTS 263,948 Great Britain Jan. 10, 1927

